Photographic materials are generally produced by coating at least one light-sensitive layer on a plastic film support. Commonly employed plastic films are cellulose plastics such as triacetyl cellulose (hereinafter abbreviated as TAC) and polyester plastics such as polyethylene terephthalate (hereinafter abbreviated as PET).
A PET film has recently been substituted for a TAC film because of its excellent productivity, mechanical strength and dimensional stability. In spite of these excellent properties of PET, the range of use of a PET film has been limited because it exhibits curling acquired during storage in the widely used roll form even after development processing, giving rise to handling problems.
In general, the forms of photographic materials are divided into sheets, such as X-ray films, plate making films, and cut films; and rolls, such as color or black-and-white negative films, 35 mm or less, packed in a cartridge to be loaded into ordinary cameras.
A TAC film chiefly used as a support for roll films are characterized primarily by outstanding superiority in freedom from optical anisotropy and transparency and also by its ability to eliminate curling during development processing. That is, since a TAC film exhibits relatively high water absorption for a plastic film due to its molecular structure, the molecular chain, once fixed by curling that has occurred with time during storage in a roll form, is re-arranged upon absorption of water during development processing whereby the curling can be eliminated. When a photographic material using a support that does not have this recovery property is used in a roll form, various problems arise such as scratching, smearing, and jamming in a printer after development.
On the other hand, to cope with the recent diverse use of photographic materials, marked advancements have been made in speeding up film feeding during photographing, increasing magnification, and reducing the size of cameras. Supports of photographic materials meeting these advanced techniques are required to have sufficient strength, sufficient dimensional stability, and reduced thickness.
In a conventional cartridge system for roll films, the film is wound around a spool not tightly but loosely, and the end of the roll film cannot be wound off the cartridge simply by turning the spool to the direction opposite to the winding direction. Therefore, the roll film has its end previously taken out of the cartridge to an appropriate length so that a photographer may fit the film end into a film feeding mechanism of a camera. However, the operation of fitting the film end into a feeding mechanism is not only troublesome but needs some skill, often resulting in a mistake, such as exposure of an intact film. Hence, there is an increased demand for a new type of camera system or cartridge system needing no such an operation. Establishment of such a system would lead to camera size reduction and ease in operation and make information recording feasible.
In these new systems, films comprising a thin support having a recording layer on the entire surface thereof or on the part of the surface thereof are utilized. Thus, films for use in these new systems must have higher mechanical properties than previciously used.
Recently developed systems include a cartridge system for easier camera loading, in which the spool of a cartridge, when loaded into a camera, is momentarily turned by a motor provided within the camera so that the film is automatically fed out. While the above-discussed curling has been a great problem confronting roll films in the conventional cartridge, the problem becomes acuter with the newer cartridge systems because the films must be tightly wound around the spool and therefore curl more readily undergo than in a conventional cartridge.
Under the present situation, however, a TAC film is brittle due to its rigid molecular structure and is not suitable for the above-described use. A PET film, though excellent in mechanical properties, cannot be used due to residual curling after development processing.
In order to endow PET with curling elimination properties, it has been proposed to copolymerize PET with an aromatic dicarboxylic acid having a metal sulfonate group and an aliphatic dicarboxylic acid having from 4 to 20 carbon atoms to produce water-absorbing PET as disclosed in JP-A-1-244446 (the term "JP-A" as used herein means an "unexamined published Japanese patent application"). The thus produced water-absorbing PET film exhibits improved curing elimination but, in turn, has a decreased heat distortion temperature, i.e., insufficient heat resistance.